Electric heating device.



L. F. PARKHURSY.

ELECTRIC HEATING DEVlCE.

APPLICATION man JULY 23,1914.

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MOT/s155555' ffm/5570A. BYwK/Ug, /g ff/5A TTURNEK kUNITED STATES PATENTOFFICE.

LEON F. PARKHURST, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GEERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC HEATING DEVICE.

Specification of Letters Patent. Patented Feb. 19, 1918.

Application led July 23, 1914. Serial No. 852,603.

To all whom t may concern:

Be it known that I, LEON F. PARKHURsT, a citizen of the United States,residing at Pittsiield, county of Berkshire, State of Massachusetts,have invented certain new and useful Improvements in Electric HeatingDevices, of which the following is a specification.

My invention has reference to the manufacture of electric resistanceheating units, and more particularly to such as are provided with a flatheating surface and which may either be used independently as a stove orheater, or in conjunction with other heat ing apparatus. In devices ofthis character, it is, of course, necessary that the resistance membershould he thoroughly insulated from the metallic parts of the heatingdevice, and at the same ztime it is highly desirable that it should bein intimate thermal relation with the supporting metal plate in orderthat the thermal drop between the resistance inember and the heatingsurface may not be so reat as to require the heating element to e run ata temperature under which it rapidly deteriorates in order to producethe desired temperature at the working surface.

' In one of its aspects, my invention has for its object the provisionof a novel structure for securing the heating unit in intimate thermalrelation with the plate and the method of producing this structure. Myinvention also provides simple and elicient means for largelyrestricting the amount of heat that is conducted from the workingportion of the plate to the edges thereof and from thence to the supportfor the plate, thereby greatly decreasing the losses and adding to theeiiiciency of the device.

Another object of my invention is the provision of a heating device ofthe character indicated, which issimple, compact and eiii cient inoperation.

Other novel features of my invention will be apparent from thedescription and will be fully pointed out in the claims.

For a fuller understanding of my'invention, reference may be had to theaccompanying drawing, in which Figure 1 is a vertical section of aheating device embodying my invention, and Fig. 2 is a sectional viewshowing more in detail the structure of the heating unit and of theparts by which the same is secured to the top plate.

Referring now to the drawings, l is a continuous freely exposed metallicflat top plate which may conveniently be made of sheet steel the surfaceof which is prefer* ably treated by any known process to preventcorrosion, and is provided with a corrugation 2 which will ordinarily beannular in form. The heating unit A is preferably formed of a resistanceelement 3 surrounded by insulation Ll which is in turn inclosed in acontinuous metallic sheath 5. The unit may be made by sii/aging orotherwise working down an ingot in a manner nonT well understood in theart. W'hile the unit may be secured-directly to the top plate, I preferiirst to place the same between two perforated plates 6 and 7 of a sizeto be received within the annular corrugation 2. The plate l is nowinverted and the plates 6 and 7, with the heating unit A arrangedbetween the same, preferably in the form of a helical coil, are placedwithin its pan-shaped center, brazing material is placed upon the whole,and the parts thus assembled are placed in a suitable furnace when thebrazing material will melt and flow through the openings of the plates 6and 7 and between the coils of the unit A, thereby firmly inclosing theplates with the heating unit against the top plate and affording a goodheat conducting path between the unit and the top plate. The brazingmaterial, solidified in the openings of the plates 6 and 7 and betweenthe coils of the heating unit, is indicated by the reference numeral 8.The brazing material also runs between the plate 6 and the plate 1 sothat a thin lm is formed between these plates and the structurecomprising the perforated plates 6 and 7 and the heating unit A arewelded or alloyed to the top plate l at every point. While the heatingunit may be secured directly to the top plate, I find in practice thatthe brazing operation which I usually utilize in securing the unit tothe plate is apt tovresult in the warping of the top plate due to.thediiierence in the coeiiicients of expansion between the top plateand the brazing material. The construction which I have above describedleaves the top plate perfectly flat, as it will be seen that the brazingmaterial touches the top plate only at separated points, and, since theplat-es G and 7 are made of a metal having substantially the samecoefficient of eX- pansion as the top plate, it is obvious that screws19.

the expansion of the plates with the heating1 unit and the brazingmaterial secured thereto as a whole will be substantially the same asthat of the top plate, and the top plate will remain dat throughout theprocess of manufacture.

The heating unit il i is provided with free ends 9 bent at richt 'i oangles to the plane or the top plate and preferably having the ends ofthe resistance conductors bared at 10.. These terminals are preferablyformed larger than the resistance conductor and may be made inaccordance with the method. described in a patent issued to lll. WhitneyApril 14th, 191e, lilo. 1,093,512.

have here shown three different terminals in order that differentdegrees of heat may be produced. Any desired number of terminals may, ofcourse, be used.

il; second imperforate plate 13 is bent upwardly at A, reilereddownwardly at 15 and engages the inner edge of the downwardly turnedportion 12 of the top plate, and the two are secured together as bywelding, the flanges of the two plates thus constituting a support forthe device, which may be received in an opening in the top of a andallows of small heat conduction into said range top. et the same timethe main portion of the plate 13 is spaced from the top plate to form achamber' forthe reception of a heat insulating material. rlhis plate isprovided with an opening 16 through which a terminal block 17 passes.This bloclr is provided with a iiange 18 by which the same is secured tothe bottom plate and to an annular ring 2O located within the bottomplate 13 by means of rlhe terminals 10 of the resistance unit are joinedto outer terminals 21 by means of conductors 22, which may be brazed orotherwise secured to the terminals 9. When the parts thus far describedhave been assembled, the insulating material 23, which is preferably inpowdered form and which may be of a composition disclosed in Patents1,072,413 and 1,072,414, which were issued to "Walter Arthur, Septomber9, 1918, is dusted into the space between the heating unit and thebottom plate through the terminal block. rlhe space within the terminalblock surrounding the terminals 9 of the sheathed wire and theconductors 22 is then lled with any suitable material, such as cement,and the bottom of the terminal block is then closed by a separatesection 25 secured to the main portion of the terminal block by screws24.,

rl`he corrugation formed in the top plate not only serves the purpose offorming a dish when the top plate is inverted and thus confines thebrazing material to the parts where the same is utilized, but a moreimportant feature and a permanent advantage range. rlhis support is oflimited area the corrugation is that it interposes a space of highthermal resistance between the heating unit and the edge of the topplate and the stove, and it thus serves to greatly reduce 'the heatlosses. Furthermore, this corrugation strengthens t-he top plate, andthe groove formed thereby acts as a receptacle for the reception of anynaaterial that may boil over from a vessel lo cated on the heating unitand thereby tends to prevent it from ruiming between the heating deviceand the stove top and eventually reaching the electric connections.

ln accordance with t-he provisions of the patent statutes, l havedescribed the principle of operation of my invention, together with theapparatus which l now consider to represent the best embodiment thereof;but l desire to have it understood that the apparatus shown is onlyillustrative, and that the invention can be carried out by other means.

llhat l claim as new and desire to secure by Letters Patent of theUnited States, is

l. ln an electric heater comprising a substantially flat freely exposedtop plate of good heat conducting material, a supporting' edge for saidplate, a heating unit mounted in close thermal relation to said plateand means for reducing the flow of heat from the unit to the supportingedge comprising a corrugation between the heated surface and the edge.

Q. An electric heater comprising a sub stantially fiat freely exposedtop plate of good heat conducting material, a supporting edge for saidplate, a heating unit mounted in close thermal relation to said plateand means for reducing the flow of heat from the unit to the supportingedge comprising a bend in the plate below the heated surface and betweenit and the edge.

8. The method of making a heating device comprising a continuousmetallic plate and a sheathed resistance heating unit which consists informing a continuous corrugation upon the plate, and brazing the heatingunit to the plate within the portion embraced by the corrugation.

rihe method of making a heating unit in which a continuous metallicplate, two perforated metallic plates and an insulated heating unit areutilized in its formation, which consists in assembling upon thecontinuous plate the perforated plates with the heating unit between andthen causing brazing material to flow into the openings of theperforated plates and around the heating unit thereby anchoring thecontinuous plate, the perforated plate and the heating unit together.

5. The method of making a heating unit in which a continuous metallicplate, two perforated metallic plates and an insulated heating unit areutilized in its formation,

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which consists in forming a continuous corrugation on the continuousplate, inverting the same, assembling the perforated plates with theheating unit therebetween upon the continuous plate within the portionof the plate embraced by the corrugation and causing brazing material toflow into the openings of the perforated plates and around the heatingunit.

6. In an electric heater, an envelop comprising upper and lower spacedmetallic plates having their edges brought into engagement, securedtogether and bent downwardly to form an extension for supporting theunit.

7. 4An electric hot plate comprising a substantially fiat upper metallicplate and a lower metallic plate having their edges brought intoengagement, secured together and bent downwardly to form an extensionfor supporting the hot plate, said extension being located above thebottom of the plate, and an electric heating element supported by saidupper plate.

8. An electric hot plate comprising a substantially flat upper metallicplate and a lower metallic plate having their edges brought intoengagement secured together and bent downwardly to form an extension forsupporting the upper plate, said eXtension being located above thebottom of the plate, an electric heating element comprising sheathedwire associated with said upper plate, the terminals of the wire beingbrought downwardly through the bottom plate.

9. In an electric heater, an envelop comprising a substantially fiat topplate and a lower plate having its edges secured to said top plate, aheating unit intimately secured to the. under side of said top plate,the top plate being provided with an annular depression surrounding saidheating unit, and a powdered heat insulating material lling the spacebetween the two plates.

10. A heating device comprising an envelop formed of spaced metallicplates hav ing their edges secured together, an insulated resistanceheating unit inclosed within a continuous metallic sheath which issecured to the under side of the top plate, a terminal block secured tothe other plate and a thermal insulating material filling the spacebetween the two plates.

In witness whereof, I have hereunto set my hand this 21st day of July.1914-.

LEON F. PARKHURST. Witnesses: y

A. R. NUGENT, A. E. CoLvrN.

